This invention relates to a seal device which can be suitably applied, for example, to a bearing system of a working mechanism on a hydraulic excavator or other construction machines.
In the case of construction machines like hydraulic excavators, bearing systems are generally employed for pin joint portions in pivotally connecting boom, arm and bucket of a front working mechanism (e.g., as disclosed in Japanese Patent Laid-Open No. H6-159346).
According to the first prior art just mentioned, a bearing system is constituted by a boss member which is provided on a boom, arm or bucket, that is to say, on one of two members to be pivotally connected with each other, a bush member which is fitted on the inner peripheral side of the boss member, a pair of brackets provided on the other one of the two members in confronting positions relative to the opposite ends of the boss member, and a shaft which is provided between the two brackets as a joint shaft for pivotally connecting the boss to the brackets.
Further, the joint shaft is placed in tubular collars which are fitted on the inner peripheral side of the brackets. Provided between the collars and bush are a tubular thrust ring which is fitted on the outer periphery of the joint shaft in such a way as to secure an axial gap space between the boss member and each bracket, and a seal ring which is attached to the collar at a position radially outward of the thrust ring to seal up a gap space between the bush and each collar.
In the case of the above-described first prior art, in order to ensure smooth rotational movements of the boss member and brackets, contacting surfaces of the bush and joint shaft are maintained in a lubricated state by supplying thereto a lubricant oil from outside intermittently at predetermined time intervals during operation of the hydraulic excavator. The seal ring is provided with a lip portion in sliding contact with an end face of the bush thereby to prevent leaks of the lubricant oil through a gap space between the bush and collar.
However, in the case of the above-described first prior art, the lip portion of the seal ring is simply held in sliding contact with an end face of the bush, so that it is still probable for the lubricant oil to leak to the outside through a clearance between the bush and collar, necessitating to supply the lubricant oil at shorter time intervals.
On the other hand, for the purpose of elongating the time intervals of the lubricant oil supply as much as possible to provide an almost lubrication-free bearing system, there has been known the second prior art bearing system employing a bush which is formed of porous sintered metal material, having a highly viscous lubricant oil impregnated into pores in its body (e.g., as known from Japanese Patent Laid-Open No. H8-105444).
In this case, the viscous lubricant oil which has been impregnated into pores of the bush is markedly reduced in viscosity under the influence of the heat of friction which is generated by sliding movements (rotation) of the joint shaft within the bush, and as a result begins to exude out of the pores to sliding surfaces between the bush and joint shaft to form a lubricating-oil film thereon.
In this connection, according to the above-mentioned first prior art, a thrust ring and a seal ring are interposed between the bush and each collar, thereby preventing sliding contact of axial end faces of the boss member and brackets by means of the thrust ring. However, it is difficult to suppress leaks of the lubricant oil through gap spaces between the bush and collars because the lip portion of the seal ring is simply held in sliding contact with an end face of the bush as mentioned hereinbefore. Therefore, for compensating leaked lubricant oil, the bearing of the first prior art necessitates to replenish the oil repeatedly from outside at shorter time intervals.
On the other hand, according to the second prior art, a resilient oil shield member and a dust seal are provided at opposite axial ends of the boss member thereby to prevent leakage of the impregnated lubricant oil in the bush.
However, since the viscosity of the impregnated lubricant oil in the bush is lowered by the heat of friction resulting from sliding movements of the joint shaft within the bush, the provision of the oil shield member and dust seal member as in the second prior art is insufficient for suppressing leaks of the lubricant oil to the outside through a gap space between the oil shield member and the joint shaft and a gap space between the dust seal and the joint shaft. As a result, outer surfaces of the bearing system are covered with leaked lubricant oil to invite deposition of dust and dirt which degrades the appearance of the bearing to a detrimental degree.
Further, in order to prevent leakage of the above-mentioned lubricant oil, it is conceivable to use an oil seal in addition to the dust seal. In such a case, however, it is probable that smooth supply of a lubricant oil is hindered by air which is trapped in the oil seal at the time of supplying a lubricant oil to the gap space between the bush and joint shaft from outside by the use of a grease gun.
In view of the above-discussed problems with the prior art, it is an object of the present invention to provide a seal device for a pin join bearing system, which can prevent leaks to the outside of a lubricant oil which is supplied to sliding surfaces between a bush and a shaft.
It is another object of the present invention to provide a seal device, which permits to supply a lubricant oil to a gap space between a bush and a shaft smoothly from outside and to complete the supply of lubricant oil efficiently within a shortened period of time.
According to the present invention, in order to solve the above-stated objectives, there is provided a seal device for a bearing system having a tubular bush member fixedly fitted in a boss member and having a shaft relatively rotatably passed through the bush member.
The seal device according to the present invention is characterized by the provision of: a first seal ring having a tubular body fitted on the outer periphery of the shaft and having a seal surface provided on an end face at one axial end of the tubular body and a lip portion provided at the other axial end for sliding contact with an end face of the bush member; and a second seal ring fixedly fitted in the boss member radially on the outer side of the first seal ring and having a tubular body fitted in the inner periphery of the boss member and a sliding surface provided at one axial end of the tubular body for sliding contact with the seal surface on the side of the first seal ring.
With the arrangements just described, the first seal ring which is fitted on the circumference of the shaft is provided with an annular seal surface on an end face at one axial end thereof, and the lip portion which is provided at the other axial end is held in sliding contact with an end face of the bush. Therefore, a lubricant oil which is supplied to contacting surfaces between the bush and the shaft is prevented from leaking to the outside by the lip portion of the first seal ring. Besides, since the second seal ring is provided with a sliding surface at one axial end thereof for sliding contact with the seal surface of the first seal ring, gap spaces between the first and second seal rings can be sealed up through two stages. Therefore, should a lubricant oil leak through a gap space between the lip portion of the first seal ring and the bush, it is prevented from leaking to the outside through gap spaces between the first and second seal rings.
In a preferred form of the present invention, the first seal ring is constituted by a lip seal having a tubular body portion provided at one axial end thereof and fitted on the outer periphery of the shaft, and the lip portion provided at the other axial end and extended toward the end face of the bush member, and a slide member located on the side of the one axial end of the tubular body portion of the lip seal and provided with the seal surface on an end face at one axial end thereof for sliding contact with the second seal ring.
In this case, the first seal ring is constituted by a lip seal and a slide member. Accordingly, by the seal surface which is formed on an end face of the slide member is held in sliding contact with the second seal ring, a gap space between the first and second seal rings is sealed up in a reliable manner. At the time the boss member is put in rotation relative to the other joined part, the sliding resistance between the slide member on the first seal ring and the second seal ring is reduced to ensure smooth sliding movements of the first and second seal rings through the slide member. Further, the lip portion of the lip seal, which is extended axially from the other axial end of the tubular body portion, can be held in sliding contact with the end face of the bush in a stable state to provide a good seal between the lip portion and the bush.
In another preferred form of the present invention, the lip seal of the first seal ring is formed of a resilient synthetic resin material, while the slide member is formed of a self-lubricating synthetic resin material. Accordingly, the lip seal is resiliently deformable, and the slide member is imparted with self-lubricating properties.
In a further preferred form of the present invention, the slide member is constituted by a tubular portion fitted on the outer peripheral side of the tubular body portion of the lip seal, and an annular portion extended radially inward from one axial end of the tubular portion to form the seal surface covering an end face portion of the tubular body portion. Accordingly, at one axial end, the slide member can cover the tubular body portion of the lip seal, and the seal surface can be formed on an end face of the annular portion.
In still another preferred form of the present invention, the second seal ring is constituted by a tubular portion fixedly fitted in the inner peripheral side of the boss member in such a way as to circumvent the first seal ring from radially outside, and an inward collar portion projected radially inward from one axial end of the tubular portion to retain the first seal ring in position in the axial direction between itself and an end face of the bush member, the inward collar portion having the sliding surface held in sliding contact with the first seal ring through the seal surface of the latter.
In this case, by the inward collar portion of the second seal ring which is held in sliding contact with the seal surface of the first seal ring, the first seal ring can be retained in position in the axial direction between the inward collar portion of the second seal ring and the end face of the bush member and at the same time a good seal can be formed therebetween.
In a further preferred form of the present invention, the second seal ring is formed of a harder material as compared with the first seal ring. Therefore, the first seal ring can be resiliently held in sliding contact with the hard second seal ring thereby to enhance the seal strength as well as the sliding performance quality of the first and second seal rings.
In a further preferred form of the present invention, an annular thrust washer is provided on the end face of the bush member for sliding contact with the lip portion of the first seal ring. Therefore, as the boss member is turned relative to the other joint member, the lip portion of the first seal ring is allowed to slide smoothly along the surface of the thrust washer which is provided on the end face of the bush.
In a further preferred form of the present invention, an annular thrust washer is provided on the side of the second seal ring for sliding contact with a seal surface of the first seal ring. Accordingly, as the boss member and the other joint member are turned relative to each other, the first seal ring is allowed to slide smoothly along the surface of the thrust washer which is provided on the side of the second seal ring.